Taxpayers would pay up to $23.6 billion for Australia to meet international climate targets if the Turnbull government were to continue with its "direct action" emissions-reduction fund as its main policy.
Following a request by the Greens, the federal Parliamentary Budget Office estimated the cost of using the fund to meet the target the Coalition submitted at the Paris climate summit - a 26 to 28 per cent emissions cut compared with 2005 levels by 2030.
The fund pays businesses and farmers through an auction process, with the cheapest bids winning contracts to cut emissions.
Contracts worth $2.23 billion have been awarded over the past two years, much of them to companies planting trees or stopping vegetation being cleared.
Despite this, government greenhouse accounts released in December showed national emissions were rising. There is only $300 million remaining in the fund, and no extra money was committed in this month's budget.
The budget office analysis found that using the fund alone to meet the emissions target would require $559 million over the next four years, and about $23 billion in the decade from 2020-21.
It comes as the government is holding two reviews into climate change and energy policy - one by Chief Scientist Alan Finkel and the other by the Environment Department.
Greens climate spokesman Adam Bandt said the Parliamentary Budget Office analysis showed the emissions reduction fund was "an empty vessel built to appease the Trumps in the Coalition".
"The government should dump [former prime minister] Tony Abbott's emission reduction fund and put in place a proper mechanism for cutting pollution, such as a carbon price, and extend the renewable energy target," he said.
Environment and Energy Minister Josh Frydenberg said asking the budget office to cost the emissions reduction fund as the only mechanism to reach the 2030 target was "a ridiculous notion, and quite ignorant".
He said the government had several other measures to cut emissions, including a plan to boost national energy efficiency, steps to phase down hydrofluorocarbons??? and the 2020 renewable energy target.
The government's emphasis has shifted since 2015, when then environment minister Greg Hunt described the emissions reduction fund and related safeguard mechanism - meant to put a limit on the emissions from big polluters - as "a plan for the next half century".
At the time, Mr Hunt said the safeguard mechanism was designed so it could be tightened after 2020 and reduce emissions - a step that would have effectively transformed it into an emissions intensity scheme.
But this path was blocked last December, when Prime Minister Malcolm Turnbull ruled out any form of carbon trading - including an emissions intensity scheme covering electricity plants, the model favoured by business groups as the cheapest available to cut emissions - following backbench anger over the suggestion a return to carbon pricing would be even considered in a policy review.
On Monday, Mr Frydenberg said Australia had a strong track record on emissions targets. It met its 2012 goal under the Kyoto Protocol (an 8 per cent emissions increase after 1990) and was on track to "meet and beat" the 2020 target (a 5 per cent cut compared with 2005).
He said the emissions fund had been highly successful, with contracts signed to reduce emissions by 189 million tonnes at an average price of $11.83 a tonne.
"We are continually reviewing our policy settings to ensure they remain effective through the 2017 climate change review and the Finkel review," he said.
Consultants Reputex released an analysis on Monday suggesting Australia could cut emissions by 45 per cent by 2030 at no net cost to business by making the cheapest cuts available.
Most of the reduction would be from the land - through tree planting and better farming - and in the electricity sector, accelerating the shift to wind and solar power. It found the target could be met at a cost of less than $20 a tonne of emissions.